According to Reuters, Ashton said the mass death sentence breached international law and urged Cairo authorities to ensure defendants' rights to a fair and timely trial.

"These mass trials are clearly in breach of international human rights law," the EU's Catherine Ashton said in a statement quoted by the news agency.

"The exact charges against each defendant remain unclear, the proceedings lack the most basic standards of due process and the verdicts appear grossly disproportionate, failing short of complying with the principle of individual sentencing," she said.

Ashton said the EU was concerned about Egypt's compliance with its international human rights obligations, as well as "the seriousness of Egypt's transition towards democracy."

"The EU calls on the Egyptian authorities to immediately reverse this trend which jeopardizes any prospects for overcoming divisions within society and to ensure progress towards a truly democratic, stable and prosperous Egypt," she said.

The comments come a day after an Egyptian court sentenced the leader of the outlawed Muslim Brotherhood, Mohammed Badie, and 682 supporters of the Islamist group to death.

The defendants were charged with crimes including inciting violence following the army overthrow of former Muslim Brotherhood President Mohammed Morsi.

The same court last month sentenced 529 Muslim Brotherhood supporters. That mass sentencing was condemned by the West, with the United States warning Egypt that executing supporters of the Muslim Brotherhood may affect the aid that Washington provides to Cairo.

The United States denounced Monday’s verdict as well, with the White House saying it was “deeply troubled”. On Tuesday, Senator Patrick Leahy announced he would not approve sending funds to the Egyptian military because of the "sham trial", as he put it.

Ashton’s comments came several hours after the German foreign ministry said it summoned the Egyptian ambassador to urge the lifting of the 683 death sentences.

According to AFP, the ministry said its Middle East coordinator Volkmar Wenzel had made the "urgent appeal" to Ambassador Mohamed Higazy for the justice authorities to reverse Monday's decision "and allow the affected people to have a fair trial".